Study On Fabrication And Interface Behavior Of AlCoCrFeNi High Entropy Alloy Particles Reinforced Al Matrix Composites

Owing to poor wettability,weak interface and poor plastic deformation coordination capability betweeen the ceramic particles.Ceramic particles reinforced Al matrix composites always suffered from the sharp decrease in the ductility.High entropy alloy（HEA）became a promising candicate for the reinforcement of Al matrix composites because of high hardness strength and thermal stability.In this paper,Al Co Cr Fe Ni HEA particles were used as the strengthening phase,5083Al aluminum alloy were used as the matrix,and HEA particle-reinforced Al matrix composites were prepared by spark plasma sintering technology and submerged/friction stir processing technology.The research results could broaden the strengthening and toughening methods of Al-based composites,and provide theoretical support for the further development of HEA/Al composites.In this paper,ABAQUS finite element method was used to establish the tensile mechanical behavior model of the HEA/Al composites with different HEA particle size,morphology and interfacial bond strength.The relationship between the particle size,morphology,interface strength,interfacial damage behavior and the mechanical properties was studied.In the SPSed HEA/Al composites prepared by spark plasma sintering（SPS）,the HEA-Al interface structure,micro-nano mechanical properties,interface stress distribution characteristics and mechanical properties of the SPSed HEA/Al composite were studied,and the fracture mechanism of the SPSed HEA/Al composite was investigated.The grain refinement mechanism,recrystallization behavior,interface formation mechanism and strengthening mechanism of SFSPed/FSPed HEA/Al composites fabricated by submerged/friction stir processing are explored.ABAQUS numerical simulation results showed that for cubic and spherical particle reinforced composites,small particles exhibit higher strengthening effects,and with the decrease of interface bonding strength,the strength and plasticity of composites are more and more sensitive to changes in particle size.Under ideal interface conditions,the strengthening effect of spherical particles is lower than that of cubic particles,but under strong and weak interface conditions,spherical particle reinforced composites exhibit higher strength and elongation;under the same conditions,interface damage is preferred ccurs in cubic particle reinforced composite materials,and has a faster expansion rate.The microstructure characterization and mechanical properties test results of the SPSed HEA/Al composites showed that the reaction of between HEA particles and Al matrix are violent,the thickness of the interface layer is about 10μm;the interface reaction products includes Al₁₃（Co Cr Fe Ni）₄,Al₉（Co Fe Ni Mg）₂ And Al₁₈Cr₂Mg₃;the average grain size of 10 vol.%HEA/Al composite is 4.73μm,the large-angle grain boundary ratio of the composites is 84%,and a recrystallized grain ratio of the composites is 78.9%.After addition of HEA particles,the yield strength of the composites increases,and the tensile strength and elongation of the composites were decreased.The HEA-Al interface fracture occurs at the interface reaction layer near the HEA particle side of,which is brittle fracture.The micro-nano mechanical properties test of the interface micro-area of the SPSed HEA/Al composite and the numerical simulation analysis results of ABAQUS showed that the interface bonding strength of the reaction layer near the HEA particle side in the SPSed HEA/Al composite is lower than that of the reaction layer near the Al matrix side.The existence of an excessively thick interface reaction layer weakens the strengthening effect of HEA particles,and on the other hand aggravates the stress concentration of the particles,the matrix and the interface area,thereby deteriorating the mechanical properties of the material.The microstructure characterization and mechanical properties test results of the FSPed HEA/Al composite material showed that the interface reaction is effectively suppressed by adjusting the HEA-Al interface structure.The thickness of the reaction layer is about 750 nm.The Al₁₃Co₄ type phase is formed earlier than the Al₉Co₂ type phase.The combination of continuous dynamic recrystallization mechanism,particle-promoting nucleation mechanism and Zener-pinning effect can be responsile for the refined grain size about 2.4μm.The tensile strength and yield strength of the 10 vol.%HEA/Al composites are 388MPa and 202 MPa,respectively,and the elongation is 15.3%.The fracture surface of the HEA-Al interface is dominated by ductile fracture,but there are still brittle fracture characteristics.The microstructure characterization and micro-nano mechanical properties,tensile properties and wear performance test analysis results of the SFSPed HEA/Al composites showed that the addition of HEA particles weakens the orientation of the Al matrix,refines the grain size of the composites（the average grain size is about 1.2μm）,and improves the micro-hardness,nano-hardness,elastic modulus,elastic strain failure resistance（H/E）and plastic deformation resistance（H³/E²）of the composites.The tensile strength and yield strength of the SFSPed HEA/Al composite are 401 MPa and 219 MPa,respectively,and the elongation rate can reach 18.9%.The fracture surface of the HEA-Al interface exhibits obvious ductile fracture.The interface microstructure characterization of SFSPed HEA/Al composites,the study of the interface behavior of FSPed/SFSPed HEA/Al composites,and the analysis of the strengthening mechanism of SFSPed HEA/Al composites showed that:In SFSPed HEA/Al composites,the interface reaction layer is composed of nano twin structure FCC phase,Al₁₈Cr₂Mg₃ and Cr-poor nano HEA particles,and the thickness is about 200 nm.The low effective Gibbs free energy of Al₉Co₂ type and Al₁₃Co₄ type phases in the interface products of FSPed HEA/Al composites is the thermodynamic nature of their formation.In SFSPed HEA/Al composites,the reduced peak temperature,shortened high-temperature residence time,smaller element diffusion coefficient,and solid solubility of alloying elements in the Al matrix enable the preservation of the FCC phase solid solution at the interface.In the FSPed/SFSPed HEA/Al composites,the formation of the interface product Al₁₈Cr₂Mg₃ can be attributed to the lower Gibbs free energy change in thermodynamics and the segregation of alloying elements in kinetics.The main strengthening mechanisms of SFSPed HEA/Al composites are load transfer strengthening,fine grain strengthening and dislocation strengthening.